Answer:
Both realized niche and fundamental niche are similar in size.
Step-by-step explanation:
If Chthamalus’ and Balanus’ respective niches were a result of niche differentiation so we can say that Chthamalus’ realized niche is not smaller than its fundamental niche. It will be of the same size because of no interspecific competition with Balanus. The whole fundamental niche is considered the niche of the Chthamalus' alone due to no competition with Balanus' for resources present in the ecosystem.